Modified three rail shear fixture (ASTM D 4255/D 4255M) and an experimental study of nonlinear in-plane shear behaviour of FRC

In order to understand the nature of nonlinearity in the in-plane shear behaviour of fibre reinforce composites (FRC), experimental data of such materials under loading cycles, involving loading, unloading, reversed loading and unloading from reversed loading, are essential. Using the standard ASTM D 4255/D 4255 M method, it will require the fixture to be subjected to tension as well as compression. It has been proven in this paper that the standard ASTM D 4255/D 4255 M fixture is incapable of delivering such data as premature buckling is expected when the fixture is under tension, even though it claimed that the fixture could be loaded in tension as well as in compression. A cyclic rail shear fixture (CRSF) as a modified version of ASTM D 4255/D 4255 M fixture has been proposed in this paper and it has been designed and manufactured. The new fixture, which maintains all the capabilities of its standard counterpart, is truly capable of sustaining loading in tension as well as in compression so that specimens can be tested for loading and reversed loading. A series of experiments have been carried out using the new fixture to characterise the nonlinear in-plane shear stress–strain relationship of unidirectional fibre reinforced composite specimens under various cyclic loading conditions. Some new experimental data of this nature are presented in this paper, which are novel in contents and crucial in guiding the formulation of theoretical models for the nonlinear behaviour of in-plane shear for general applications.